Back to EveryPatent.com
United States Patent |
5,267,031
|
Katoh
,   et al.
|
November 30, 1993
|
Color image processing apparatus
Abstract
There is provided a color image processing apparatus comprising color
conversion circuit for converting image data to a desired color, feature
extraction circuit for extracting a feature of the image data and image
correction circuit for correcting the image data on the basis of the
feature extraction circuit, characterized in that a color conversion
processing is executed prior to extraction of feature from the image data.
Inventors:
|
Katoh; Koichi (Yokohama, JP);
Ikeda; Yoshinori (Kawasaki, JP);
Kurita; Mitsuru (Higashi, JP);
Ichikawa; Hiroyuki (Kawasaki, JP)
|
Assignee:
|
Canon Kabushiki Kaisha (Tokyo, JP)
|
Appl. No.:
|
584644 |
Filed:
|
September 19, 1990 |
Foreign Application Priority Data
| Nov 14, 1988[JP] | 63-287091 |
Current U.S. Class: |
358/527 |
Intern'l Class: |
H04N 001/46 |
Field of Search: |
358/80
|
References Cited
U.S. Patent Documents
4382981 | May., 1983 | Stoetzer et al. | 427/105.
|
4538182 | Aug., 1985 | Saito | 358/80.
|
4700399 | Oct., 1987 | Yoshida | 382/17.
|
4724477 | Feb., 1988 | Ellis | 358/80.
|
4845550 | Jul., 1989 | Urabe et al. | 358/80.
|
4873570 | Oct., 1989 | Suzuki | 358/80.
|
5142356 | Aug., 1992 | Usami | 358/80.
|
Foreign Patent Documents |
357507 | Mar., 1990 | EP.
| |
2559826 | May., 1979 | DE.
| |
3313392 | Apr., 1983 | DE.
| |
3521259 | Dec., 1985 | DE.
| |
1401301 | Apr., 1965 | FR.
| |
61-177399 | Aug., 1986 | JP.
| |
2119600 | Nov., 1983 | GB.
| |
2162716 | Feb., 1986 | GB.
| |
Other References
Trundell, Television and Video Engineers Pocketbook (1987), pp. 63-65.
|
Primary Examiner: Britton; Howard W.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper & Scinto
Parent Case Text
This application is a continuation of application Ser. No. 07/436,256 filed
Nov. 14, 1989, now U.S. Pat. No. 4,982,277.
Claims
What is claimed is:
1. A color image processing apparatus comprising:
inputting means for inputting a color image signal;
conversion means for converting said color image signal inputted by said
inputting means to a color image signal defined by standard color space;
color conversion means for performing predetermined color conversion on
said color image signal defined by standard color space converted by said
conversion means; and
color correction means for performing a color correction to output the
color image signal defined by standard color space converted by said color
conversion means to an output device.
2. A color image processing apparatus according to claim 1, wherein said
color image signal defined by standard color space is an NTSC standard
signal.
3. A color image processing apparatus according to claim 1, wherein said
inputting means comprises a color sensor.
4. A color image processing apparatus according to claim 1, wherein said
color conversion means comprises:
extracting means for extracting a signal corresponding to a predetermined
color from said color image signal defined by standard color space; and
replacing means for replacing said signal corresponding to said
predetermined color extracted by extracting means with a signal
corresponding to another color that is different from said predetermined
color.
5. A color image processing apparatus according to claim 1, wherein said
color correction means corrects said color image signal defined by
standard color space to a four color signal of yellow, magenta, cyan and
black.
6. A color image processing apparatus according to claim 5, further
comprising means for outputting a signal corrected by said color
correction means to a color printer.
7. A color image processing method comprising the steps of:
inputting a color image signal;
converting the color image signal inputted in the inputting step to a color
image signal defined by standard color space;
performing predetermined color conversion on the color image signal defined
by standard color space converted in the conversion step; and
performing a color correction to output the color image signal defined by
standard color space converted in the color conversion step to a output
device.
8. A color image processing method according to claim 7, wherein the color
image signal defined by standard color space is an NTSC standard signal.
9. A color image processing method according to claim 7, wherein the
inputting step is performed by a color sensor.
10. A color image processing method according to claim 7, wherein the color
conversion step comprises the steps of:
extracting a signal corresponding to a predetermined color form the color
image signal defined by standard color space; and
replacing the signal corresponding to the predetermined color extracted in
the extracting step with a signal corresponding to another color that is
different from the predetermined color.
11. A color image processing method according to claim 7, wherein the color
correction step corrects the color image signal defined by standard color
space to a four color signal of yellow, magenta, cyan and black.
12. A color image processing method according to claim 11, further
comprising the step of outputting a signal corrected in the color
correction step to a color printer.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a color image processing apparatus.
2. Related Background Art
Hitherto, as is also known as a color laser copier or the like, for
instance, a color image processing apparatus having a complicated editing
function, a color converting function, and the like using a digital image
processing technique has been invented.
A color image processing apparatus as shown in FIG. 3 has been proposed as
an apparatus having such character processing function, color converting
function, and editing function.
In such an apparatus, in accordance with the level of Bk which is
calculated by primary signals Y, M, and C which were color separated, the
Y, M, and C signals are subtracted and the Bk signal is increased and the
edge is emphasized in accordance with the level which is calculated from
Min (Y, M, C). Due to this, the edge portion of a black character is
replaced to a single black portion as much as possible, thereby improving
the quality of character. However, in such an image processing system, if
a color conversion circuit is arranged after the color correction circuit,
in the case of executing a color converting process to convert a chromatic
character into a black character by the color conversion, the chromatic
character cannot obviously be extracted as a black character in a black
extraction section. Therefore, subtraction amounts of Y, M, and C are
small, so that the color is detected in the color conversion section and
is color converted so as to obtain black. On the other hand, since the
value of Min (Y, M, C) is small in the black extraction section, a level
determination section reduces the edge emphasis in an edge emphasis
section as compared with the case of black.
Therefore, the ordinary black character becomes a sharp image by the edge
emphasis. However, there occurs an inconvenience such that the character
which was converted into black by the color conversion becomes a dull
character.
Although the above example has been described with respect to the image
process which is executed to a black character, even if the kind of such
an image process is another kind of process, if the apparatus is
constructed as in the conventional one, an inconvenience corresponding to
the process occurs.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an image processing
apparatus which can solve the above problems.
Another object of the invention is to provide an image processing apparatus
which can execute both of a process to extract characteristics or the like
and a color converting process.
Still another object of the invention is to provide an image processing
apparatus which can accurately extract characteristics even when executing
a process such as a color conversion or the like.
Under such objects, according to a preferred embodiment of the invention,
there is disclosed an image processing apparatus comprising color
converting means for converting image data into a desired color,
characteristic extracting means for extracting the characteristics of the
image data, and image correcting means for correcting the image data in
accordance with the characteristics extracted by the characteristic
extracting means, wherein the color converting process is executed before
the characteristics of the image data are extracted.
Further another object of the invention is to provide an image processing
apparatus which can easily execute the processes for color conversion,
character correction, and the like to a color image signal obtained by
being read.
The above and other objects and features of the present invention will
become apparent from the following detailed description and the appended
claims with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a construction of an embodiment 1 of the
present invention;
FIG. 2 is a circuit diagram of a color conversion 2;
FIG. 3 is a diagram showing a conventional example;
FIG. 4 is a block diagram of an embodiment 2;
FIG. 5 is a block diagram of an embodiment 3;
FIGS. 6, 6A and 6B are block diagrams for a black character process;
FIG. 7 is a diagram of a calculating circuit of a YIQ signal;
FIG. 8 is a diagram of a calculating circuit of an achromatic signal W;
FIG. 9 is a diagram of a black generating circuit;
FIG. 10 is a diagram of a black level determination circuit;
FIG. 11 is a diagram of an edge signal calculating circuit;
FIG. 12 is a diagram of an image area determination circuit; and
FIG. 13 is a diagram of a black character correction circuit.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
According to an embodiment of the invention which will be explained
hereinlater, there is shown an apparatus in which by using a construction
such that the color converting process is executed before the color
correcting process, the picture quality of the color converted image and
the picture quality of the image which is not color converted are
equalized, and the deterioration in picture quality due to a contradiction
when respective functions are combined is eliminated.
The invention will be described hereinbelow with reference to the drawings.
Embodiment 1
FIG. 1 shows an embodiment of the invention. Color image signals which are
obtained by converting image signals from color sensors (for instance, R,
G, B) (not shown) into digital signals by A/D converters are converted
such that white=OOH and black=FFH in accordance with the relative luminous
efficiency characteristics of the human eyes by logarithm converting
circuits. Thus, the Y, M, and C signals corresponding to the concentration
value are obtained.
The digital signals of Y, M, and C obtained from an image reading section
(not shown) are input to a color conversion section 1.
As shown in FIG. 2, in the color conversion section 1, a check is made by
three window comparators 7, 8, and 9 to see if the image data of Y, M, and
C denote the colors which are color converted or not. If they are the
colors to be color converted, a selecting signal 13 is set to the high "H"
level and preset image data Y',M', and C' after completion of the color
conversion are selected by a CPU (not shown) and the color converting
processes are executed.
In FIG. 2, Y.sub.max, Y.sub.min, M.sub.max, M.sub.min, C.sub.max, and
C.sub.min denote registers to store data which are set from the CPU
through a CPU BUS for controlling the apparatus of the embodiment.
Y', M', and C' indicate registers to store the color data of predetermined
colors after completion of the conversion. Outputs of the registers are
input to B input terminals of selectors 10, 11, and 12, respectively.
The color data of the input image are input to A input terminals of the
selectors 10, 11, and 12, respectively. Outputs of the window comparators
7, 8, and 9 are supplied to an AND gate and the AND of them is calculated.
An output of the AND gate is input to the selectors 10 to 12.
In the above construction, if the window comparators 7 to 9 determine that
the color data of the input image lies within a predetermined range which
has been set in each of the registers Y.sub.max, Y.sub.min, M.sub.max,
M.sub.min, C.sub.max, and C.sub.min, the selectors 10 to 12 are switched
so as to output the data which is input to each B input terminal, thereby
executing the color converting operation.
The outputs of the color conversion section 1 are input to a color
correction section 2 and a black extraction section 5. The color
correction section 2, black extraction section 5, a level determination
section 6, and an edge emphasis section 4 are well known.
Embodiment 2
FIG. 4 shows the embodiment 2 of the invention. Image signals from color
sensors (for instance, R, G, B) 0 are converted into digital signals by
A/D converters. The resultant color digital image signals R, G, and B are
converted into the R, G, and B signals of the NTSC by an NTSC conversion
section 17. The NTSC conversion section comprises well-known 3.times.3
primary processing circuits.
The image signals which were converted into the R, G, and B signals of the
NTSC are input to the color conversion section 1. The color conversion
section 1 is similar to that shown in FIG. 1. The color conversion in the
image signals of the R, G, and B systems can be also executed in a manner
similar to the embodiment 1 by setting corresponding parameters of the
image signals such that Y.fwdarw.B, M.fwdarw.G, C.fwdarw.R, Y'.fwdarw.B',
M'.fwdarw.G', C'.fwdarw.R', Y.sub.max .fwdarw.B.sub.max, Y.sub.min
.fwdarw.B.sub.min, M.sub.max .fwdarw.G.sub.max, M.sub.min
.fwdarw.G.sub.min, C.sub.max .fwdarw.R.sub.max, and C.sub.min
.fwdarw.R.sub.min.
After the color conversion of the RGB system was executed as mentioned
above, the resultant R, G, and B data are input to a logarithm conversion
section 16, so that the image signals of the YMC system according to the
relative luminous efficiency characteristics of the human eyes as
mentioned above are obtained.
Since the color correction section 2, black extraction section 5, level
determination section 6, and edge emphasis section 4 are incorporated in
the well-known technique as mentioned above, their descriptions are
omitted.
Embodiment 3
FIG. 5 shows an embodiment 3 of the invention. The NTSC conversion section
17, color conversion section 1, and logarithm conversion section 16 are
similar to those in the embodiment 2.
The color correction section 2 is the well-known technique and is a circuit
to correct the concentration signals of C, M, and Y into the C, M, Y, and
K signals according to an output apparatus.
FIGS. 6A and 6B show an example of a circuit construction of a black
character processing section 18. In FIGS. 6A and 6B, reference numeral 10
denotes a YIQ signal calculating circuit to calculate a luminance signal Y
and color signals I and Q from the R, G, and B signals of the color
conversion section 1. The luminance signal Y is inverted into a darkness
signal Y by an inverter 30 to obtain an edge signal of a black character.
Thereafter, the edge signal is extracted by executing the Laplacian
operation by a black edge generating circuit 40 and a KE signal is output.
The I and Q signals are signals indicative of the color differences from
an achromatic color and are input to an achromatic color signal
calculating circuit 20. An achromatic color signal W is output from the
calculating circuit 20 by using a look-up table. The W signal indicates
that the color approaches the achromatic color as the value of the W
signal is large. The W signal and Y signal are input to a black level
determining circuit 50. The circuit 50 combines the W and Y signals and
outputs a T signal. Practically speaking, the signal indicative of a
degree of black is output as a T signal by a binary or more value. The
black edge generating circuit 40 outputs black character edge signals
E.sub.1 and E.sub.2 from the black edge signal KE in accordance with the
black level signal. The E.sub.1 signal is a signal to emphasis the edge of
the black character. The E.sub.2 signal is a signal to eliminate a color
deviation of the edge of the black character. An image area signal
generating circuit 70 determines that an area of the bright chromatic
color and areas near it are an image area on the basis of the W signal and
Y signal and outputs an image area determining, signal Z. A black
character correcting circuit 80 corrects C (cyan), M (magenta), Ye
(yellow), and K (black) by using the black character edge signals E.sub.1
and E.sub.2 from which an erroneous discrimination was eliminated by the
image area signal Z. That is, the E.sub.2 signal is added as a correction
signal to the C, M, and Y signals and the E.sub.1 signal is added as a
correction signal to the K signal. The resultant corrected signals are
input to an output apparatus such as color printer like, for instance, a
color LBP 95 or the like, color monitor, or the like at the next stage.
A block of each circuit shown in FIGS. 6A and 68 will now be described.
(1) In FIGS. 6A and 6B mentioned above, reference numeral 10 denotes YIQ
signal calculating means which receives the RGB signals as input signals.
The YIQ signal calculating circuit 10 will now be described with reference
to FIG. 7. In FIG. 7, reference numerals 25, 26, and 27 denote multipliers
to multiply the RGB signals with predetermined parameters a.sub.ij (i,
j=1, 2, 3). Reference numeral 28 denotes a memory in which the parameters
a.sub.ij are stored; 29 indicates a selector to select the proper
parameters which are multiplied to the R, G, and B signals; 37 an adder to
add outputs of the multipliers 25, 26, and 27; and 38 a selector to select
an output of the adder 37 to each of the Y, I, and Q signals. The Y, I,
and Q signals are expressed by using the R, G, and B signals and the
parameters a.sub.ij as follows.
Y=a.sub.11 .times.R+a.sub.12 .times.G+a.sub.13 .times.B,
I=a.sub.21 .times.R+a.sub.22 .times.G+a.sub.23 .times.B,
Q=a.sub.31 .times.R+a.sub.32 .times.G+a.sub.33 .times.B
(2) In FIGS. 6A and 6B, reference numeral 20 indicates the achromatic color
signal calculating circuit. FIG. 8 shows an internal construction of the
achromatic color signal W calculating circuit. Reference numeral 21
denotes a multiplier to output the square of the I signal; 22 indicates a
multiplier to obtain the square of the Q signal; 23 the adder for adding
outputs of the multipliers 21 and 22 and outputting I.sup.2 +Q.sup.2 ; and
24 a look-up table to determine the output W in accordance with the result
of I.sup.2 +Q.sup.2. The output W of the look-up table 24 is determined by
the following equation.
##EQU1##
(3) In FIGS. 6A and 6B, as mentioned above, the inverter 30 inverts the Y
signal and outputs the Y signal.
(4) In FIGS. 6A and 6B, reference numeral 40 indicates the black edge
amount KE generating circuit. An internal construction of the black edge
generating circuit will now be described with reference to FIG. 9.
Reference numerals 31, 32, 33, 34, and 35 denote line buffers in which an
objective pixel is set to the center. Reference numeral 36 denotes a
computing circuit to calculate the edge amount. Assuming that values
x.sub.ij (i, j=1, 2, 3, 4, 5) have been stored in the line buffers, the
objective pixel is expressed by x.sub.33 =Y. The edge amount KE is
obtained by the following equation.
KE=x.sub.33 -(x.sub.11 +x.sub.15 +x.sub.51 +x.sub.55)/4
(5) In FIGS. 6A and 6B reference numeral 50 denotes the black level
determining circuit. FIG. 10 shows an internal construction of the black
level determining circuit. Reference numeral 51 indicates a multiplier to
multiply the signals Y and W. Reference numeral 52 represents a threshold
processing circuit for processing an output u of the multiplier 51 and
outputting the resultant data as a black level signal T in a manner such
that: 0 if u<T.sub.0 ; 1 if T.sub.0 .ltoreq.u<T.sub.1 ; 2 if T.sub.1
<u<T.sub.2 ; and 3 if T.sub.2 .ltoreq.u.
(6) In FIGS. 6A and 6B, reference numeral 60 represents a black character
edge generating circuit for outputting two kinds of edge signals E.sub.1
and E.sub.2 on the basis of the black edge signal KE and black level
signal T.
FIG. 11 shows a construction of the edge generating circuit 60. Reference
numeral 61 denotes a comparator to compare the value of the KE signal with
a threshold value stored in a memory 62. When the KE is larger than the
threshold value, 1 is output. When the KE is equal to or smaller than the
threshold value, 0 is output. Reference numeral 62 denotes the memory to
store a predetermined threshold value, and 63 indicates a processing
circuit for obtaining the edge signal E.sub.1 from the KE signal, the T
signal, and an output of the comparator 61.
Practically speaking, the processing circuit 63 outputs E.sub.1 =0 when the
output of the comparator 61 is 0 and outputs E.sub.1 =.alpha..sub.1
.times.KE when the output of the comparator 61 is 1. .alpha..sub.1 denotes
a constant which is properly decided in dependence on the value of T and
E.sub.1 is expressed. Reference numeral 64 indicates a comparator for
comparing the value of KE with a threshold value stored in a memory 65.
When the KE is larger than the threshold value, 1 is output. When the KE
is equal to or smaller than the threshold value, 0 is output. Reference
numeral 65 denotes the memory in which a predetermined threshold value is
stored. Reference numeral 66 represents a processing circuit to obtain the
edge signal E.sub.2 from the KE signal, the T signal, and an output of the
comparator 64. "0" is stored as a threshold value in the memory 65. When
the output of the comparator 64 is 0, the processing circuit 66 outputs
E.sub.2 =KE.times.(-1).times..alpha..sub.2. When the output of the
comparator 64 is 1, E.sub.2 =KE.times..alpha..sub.2 is output.
.alpha..sub.2 is a constant which is properly determined by the value of T
and E.sub.2 is expressed.
(7) In FIGS. 6A and 6B, reference numeral 70 denotes the image area signal
generating circuit. FIG. 12 shows an internal construction of the image
area signal generating circuit 70. In FIG. 12, reference numeral 71
denotes a multiplier for multiplying the Y signal and the W signal
obtained by inverting the W signal, thereby obtaining an X signal.
Reference numeral 72 denotes a threshold processing circuit for comparing
the X signal with a predetermined threshold value and outputting the
result of the comparison between them. Reference numerals 73, 74, and 75
indicate line buffers to store an output of the threshold processing
circuit 72. Reference numeral 76 represents a determining signal
processing circuit for reading out values of the line buffers 73, 74, and
75 around the objective pixel and discriminating whether the objective
pixel lies within the image area or not. If it lies within the image area,
1 is output as an image area signal Z. If the objective pixel is out of
the image area, 0 is output as the image area signal Z.
(8) In FIGS. 6A and 6B, reference numeral 80 denotes the black character
correcting circuit. FIG. 13 shows an internal construction of the black
character correcting circuit 80. Reference numeral 82 denotes a gate for
outputting 1 when the black level is not 0 and the image area determining
signal Z is 0 and outputting 0 in the other cases on the basis of the
black level signal T and the image area determining signal Z. Reference
numeral 83 indicates a selector to output E.sub.1 '=E.sub.1 and E.sub.2
'=E.sub.2 when an output of the gate 82 is 1. The selector 83 outputs
E.sub.1 '=0 and E.sub.2 '=0 when the output of the gate 82 is 0. Reference
numeral 84 denotes an adder to add the E.sub.2 ' signal to the C signal;
85 indicates an adder to add the E.sub.2 ' signal the M signal; 86 an
adder to add the E.sub.2 ' signal to the Y signal; and 87 an adder to add
the E.sub.1 ' signal to the K signal.
In the above apparatus, the edge emphasis is executed with respect to the
area which was determined to be a character portion, while the edge
emphasis is not executed with respect to the area which was decided to be
a dot color image.
Since the black character process has been executed after the color
converting process of the color conversion circuit 1 as shown in FIGS. 1
and 5, as compared with the case where the color converting process is
performed before the black character process, an erroneous discrimination
in the black character process can be prevented and the accurate process
can be executed.
In the embodiments of the invention described above, an edge of the black
or achromatic color portion has been extracted for the black character
process as an extraction of the characteristics of an image. However, the
invention is not limited to such an edge extraction. The invention can be
also similarly applied to other characteristic extracting process or the
like to extract other characteristics such that, for instance, only the
portion of a special color component is extracted and the other portions
are masked.
As described above, according to the embodiments, by executing the color
converting process before the characteristic extracting process, the
erroneous discrimination in the characteristic extraction can be prevented
and a good picture quality is obtained.
Top